1. Field of the Invention
This invention relates to acoustic type pipeline surveying, in general. More specifically, it concerns a unitary marker structure with a self-testing element in conjunction therewith.
2. Description of the Prior Art
The concept of applying markers of one sort or another to a pipeline at predetermined intervals, in order to note passage of surveying pigs or the like, is quite well known. However, in order for such a pipeline marker signal generator to be effective, it is important that the fact of continuing operation is known.
Consequently, it is an object of this invention to provide the combination of a simplified acoustic pipeline marker which includes a detector that can be momentarily energized and will pick-up the marker signal if it exists, with provision for a visual indicator.